Taking the fight to Moscow, if that means heavy bombing indiscriminately, will indicate Ukraine has sunk to the level of Russia, and has no regard for civilians lives. Moscow is full of decent people who are as victimized by Putin's autocracy as the Ukrainian people are. Two wrongs will not make a right.
Defense is a legitimate goal of war. Spilling the blood of innocent people is not.
Furthermore, any attack on Russian territory could result in them lobbing nukes, perhaps tactical nukes, perhaps city killers. Maybe y'all are just venting, but try for a second to focus on what a ruthless dictator with a huge nuclear arsenal means.